1. Field of the Invention
The present invention relates to a device for detecting abnormal heat generation of a wire harness due to e.g. rare short-circuiting, and a power supply device for a vehicle which can detect abnormal heat generation to prevent attenuation of the wire harness.
2. Description of the Prior Art
Conventionally, in a motor vehicle, generally, power generated by a power source such as a battery or alternator is supplied to respective loads through a wire harness composed of a plurality of electric wires. The wire harness 1, as shown in FIG. 11, has a structure in which a large number of core wires la are covered with an insulating covering layer 1b. Namely, the wire harness is commonly converged and protected by fitting-over of soft vinyl chloride and tape winding so that current leakage form the core wires can be prevented.
The wire harness is generally connected to a fuse. This prevents breakage of each load and deterioration of electric wires due to an excessive current generated when a voltage in a power source such as a battery and an alternator is varied or dead short-circuiting of the electric wire occurs.
Such a connection between the wire harness and the fuse can be made using a fuse box 2 as shown in FIG. 12. The fuse box 2 includes a housing 5 of insulating heat-resistance resin and a fuse element 3 housed in the housing 5. The wire harness is connected to terminals 4a and 4b provided at both ends of the fuse element 3.
As shown in FIG. 13, generally, the fuse used for a vehicle is given such a blowout characteristic as it blows out instantaneously for the current not smaller than 200% of fuse rating and is given an endurance characteristic for a rushing current smaller than 200% of the fuse rating. Therefore, when the current smaller than 200% of the fuse rating flows, the fuse has a relatively long melting time.
In a vehicle, when the insulating film 1b of the wire harness 1 deteriorates owing to time passage, or is brought into contact with both edges of the vehicle, state of xe2x80x9cdead shortxe2x80x9d or xe2x80x9crare shortxe2x80x9d (intermittent short) may result. In the case of the dead short, a large current flows through the fuse and hence the fuse blows out instantaneously. On the other hand, in the case of rare short, the fuse repeats heat generation and heat dissipation so that the time until the blowout is apt to be prolonged.
Therefore, if the rare short continues, the insulating film 1b of the wire harness 1 constitutes a heat storage body before the fuse melts down to raise the temperature. As a result, the insulating film 1b will be further deteriorated. The present invention has been accomplished in order to solve the problems described above.
A first object of the present invention is to provide an abnormality detecting device which can avoid deterioration of the wire harness due to the rare short.
A second object of the present invention is to provide a power supply device for a vehicle provided with such an abnormality detecting device.
In order to attain the first object of the present invention, there is provided a device for detecting abnormality of a wire harness for a motor vehicle comprising: a wire harness; a temperature fuse coupled with said wire harness, a corresponding region of the wire harness blowing out when abnormality occurs at a certain position of the wire harness; and means connected to the temperature fuse to detect presence or absence of break of the temperature.
In this configuration, since abnormality of the wire harness can be detected by detecting presence or absence of break of the temperature fuse, a device for detecting abnormality of the wire harness i.e. a temperature increase in of the wire harness due to rare short of the wire harness can be easily provided.
In order to attain the second object of the present invention, there is provided a power supply device for a vehicle comprising: a power supply; a wire harness connected to the power supply; a load to which a current is supplied through the wire harness; a temperature fuse coupled with said wire harness, a corresponding region of the wire harness blowing out when abnormality occurs at a certain position of the wire harness; and means connected to the temperature fuse to detect presence or absence of break of the temperature; and means for cutting off a current flowing through the wire harness when break of the temperature fuse is detected.
In this configuration, when the abnormality of the wire harness is detected by the abnormality detecting device, the current flowing through the wire harness can be forcibly cut off. This provides a power supply device which can avoid further deterioration of the wire harness.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.